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Kth Substring

Problem Statement

You are given a string s.
Among the different substrings of s, print the K-th lexicographically smallest one.

A substring of s is a string obtained by taking out a non-empty contiguous part in s.
For example, if s=ababc, a, bab and ababc are substrings of s, while ac, z and an empty string are not.
Also, we say that substrings are different when they are different as strings.

Let X = x1x2...xn and Y = y1y2...ym be two distinct strings. X is lexicographically larger than Y if and only if Y is a prefix of X or xj > yj where j is the smallest integer such that xj ≠ yj.

Constraints

1≤|s|≤5000

s consists of lowercase English letters.

1≤K≤5

s has at least K different substrings.

Partial Score

67 points will be awarded as a partial score for passing the test set satisfying |s|≤50.

Input

Input is given from Standard Input in the following format:

sK

Output

Print the K-th lexicographically smallest substring of K.

Sample Input 1

aba
4

Sample Output 1

b

s has five substrings: a, b, ab, ba and aba.
Among them, we should print the fourth smallest one, b.
Note that we do not count a twice.